This invention relates to a switching arrangement and more particularly, but not exclusively, to a switching arrangement used in a pulse modulator for providing pulses of variable length and pulse repetition frequency (PRF).
A requirement exists for pulse modulator test equipment which is suitable for supplying variable output, with operating voltages, of say up to 30 kV, duty cycles in the range of less than 1% and up to greater than 30%, pulse widths in the range of 15 ns to greater than 100 microseconds and PRFs up to 750 kHz. In conventional arrangements, a pulse transformer would be used as a modulator for driving rf sources. However, it would be difficult to design a pulse transformer which could meet the demanding requirements outlined above.
The present invention seeks to provide a switching arrangement and particularly a switching arrangement suitable for driving rf sources for test purposes. However, it is envisaged that the arrangement may also be suitable for use in other non-test applications where demanding switching requirements exist.
According to the invention, there is provided a switching arrangement comprising a solid state switch and control means arranged to apply control pulses to the solid state switch, such that when pulses of one polarity are applied, the switch is maintained in an on state and when pulses of the other polarity are applied, the switch is maintained in an off state.
Thus, by controlling the duration of the pulse train and its polarity, the switch can be controlled to give an output having characteristics which are variable over wide ranges, giving great versatility. For example, the PRF may be varied so as to give anything from a dc output to a frequency of 750 kHz. Providing pulses of one polarity continue to be applied, the switch will remain in its maintained state. The invention is thus particularly applicable for use in test equipment.
In a preferred arrangement, the control pulses are used to supply power to the switch drive circuitry. Advantageously, the switch is a power FET.
In a preferred arrangement, an H-bridge circuit is included to generate the control pulses, the H-bridge circuit including the primary winding of a transformer, and a secondary of the transformer being connected to the switch.
In a particularly advantageous arrangement, a plurality of switches are included, each switch having a respective different secondary winding connected thereto and there being a common single primary. This enables the switches to be controlled and powered simultaneously with a single input.
According to a feature of the invention, a pulse modulator includes a switch arrangement in accordance with the invention, and in another feature of the invention, test equipment includes a pulse modulator including the switching arrangement also. The invention is particularly advantageously applicable to test equipment where it is often necessary to be able to produce a wide range of outputs having very different characteristics.